Peritoneal dialysis machine

ABSTRACT

A method for operating a dialysis cassette including a flexible membrane that covers a pump chamber includes allowing a source of fluid to fluidly communicate with the pump chamber of the dialysis cassette, filling the pump chamber with the fluid from the source, mechanically extending the flexible membrane into the pump chamber with a piston head to expel the fluid from the pump chamber through a flow path, and directly sensing a pressure of the fluid flowing through the flow path at a location of the dialysis cassette adjacent to the pump chamber and using the sensed pressure to perform a test prior to delivering fluid to a patient.

PRIORITY CLAIM

This application claims priority to and the benefit of U.S. patentapplication Ser. No. 13/373,909, filed Dec. 5, 2011, entitled,“Peritoneal Dialysis Machine”, which is a continuation of U.S. Pat. No.8,070,709, filed Jul. 21, 2009, entitled, “Peritoneal Dialysis Machine”,which is a continuation application of U.S. Pat. No. 7,575,564, filedOct. 27, 2004, entitled, “Improved Priming, Integrity and Head HeightMethods and Apparatuses For Medical Fluid Systems”, which claimspriority to and the benefit of U.S. Provisional Patent Application No.60/515,815, filed Oct. 28, 2003, entitled, “Improved Priming, Integrityand Head Height Methods and Apparatuses for Medical Fluid Systems”, theentire contents of each of which are hereby incorporated by referenceand relied upon.

BACKGROUND

The present invention relates generally to medical fluid systems andmore particularly to the testing and priming of such systems.

It is known in peritoneal dialysis systems to perform integrity teststhat attempt to verify that the numerous fluid valves in a disposablecassette do not leak, that leaks do not occur between multiple pumpchambers in the cassette, that leaks do not occur across fluid pathways,and that an isolation occluder, which is intended to stop liquid flow influid lines connected to the cassette in the event of a systemmalfunction, is performing that procedure properly. In one known wetleak test described in U.S. Pat. No. 5,350,357, a disposable cassette isloaded into a peritoneal dialysis cycler and the solution bags areconnected. The test consists of the following steps:

(i) a negative pressure decay test of the fluid valve diaphragms isperformed;

(ii) a positive pressure decay test of the fluid valve diaphragms isperformed;

(iii) a positive pressure decay test is performed on the first pumpchamber, while a negative pressure decay test is performed on the secondpump chamber;

(iv) a negative pressure decay test is performed on the first pumpchamber, while a positive pressure decay test is performed on the secondpump chamber; after which

(v) both pump chambers are filled with a measured volume of fluid, allfluid valves are opened and the occluder is closed, positive pressure isapplied to both pump chambers for a period of time, after which thevolume of fluid in each pump chamber is measured again to determine ifany fluid has leaked across the occluder.

As indicated, the above testing procedure is performed after solutionbags are connected to the peritoneal dialysis system. If integrity ofthe cassette or tubing is faulty, the sterility of the solution bagsbecomes compromised. In such a case, both the disposable cassette andsolution bags have to be discarded. Additionally, it is possible thatliquid from the solution bags can be sucked into the machine's pneumaticsystem, causing the pneumatic system of the machine to malfunction.

Wet tests are also susceptible to false triggers. In particular, coldsolution used in the test causes many false disposable integrity testalarms each year because the tests fail when an occluder, which issupposed to clamp off all fluid lines, does not properly crimp or sealthe tubing lines. When the solution is cold, it cools the set tubing toa lower temperature than the tubing would be if placed only in room air.Colder tubing is harder to occlude, allowing fluid in some cases to leakpast the occluder and cause the test to fail. Once a dialysis therapystarts, the fluid passing through the tubing is warmed to about 37° C.,enabling the occluder to perform satisfactorily.

It is therefore desirable to have an integrity test that is performedbefore the solution bags are attached to the therapy machine and toeliminate the use of cold solution to prevent false triggers.

A “dry” test is described briefly in U.S. Pat. No. 6,302,653. Thedescription is based in part upon the “dry test” implemented in theBaxter HomeChoice® cycler in December of 1998. The actual testimplemented in the HomeChoice® cycler consists of four steps, the firstof which occurs before the solution bags are connected. The next threesteps require the solution bags to be connected but do not require fluidto be pulled from the bags into the machine. FIGS. 1 to 4 illustrate theareas of a fluid cassette tested by the individual steps of the known“dry” test. While the above “dry” test eliminates the problem of fluidpotentially leaking into the pneumatics of the machine, the test doesnot prevent the sterility of the bags from being compromised potentiallyupon a leak and thus from being discarded if the integrity of thedisposable cassette is compromised.

Moreover, dry testing with air is believed to be more sensitive than thewet test, which uses dialysis fluid. It is therefore also desirable tohave an integrity test that uses air for sensitivity reasons as well asfor the reasons stated above.

While integrity testing poses one problem to manufacturers of medicalfluid machines, another common problem is the priming of the fluidsystem within those machines. In many instances, air must be purged fromone or more tubes for safety purposes. For example, in the realm ofdialysis, it is imperative to purge air from the system, so that thepatient's peritoneum or veins and arteries receive dialysis fluid thatis free of air. Consequently, automated dialysis machines have beenprovided heretofore with priming systems. In peritoneal dialysis, theobject of priming is to push fluid to the very end of the line, wherethe patient connector that connects to the patient's transfer set islocated, while not priming fluid past the connector, allowing fluid tospill out of the system.

Typically, dialysis machines have used gravity to prime. Known gravityprimed systems have a number of drawbacks. First, some priming systemsare designed for specifically sized bags. If other sized bags are used,the priming system does not work properly. Second, it happens in manysystems that at the beginning of priming, a mixture of air and fluid canbe present in the patient line near its proximal end close to adisposable cartridge or cassette. Fluid sometimes collects in thecassette due to the installation and/or integrity testing of same. Suchfluid collection can cause air gaps between that fluid and the incomingpriming solution. The air gaps can impede and sometimes prevent gravitypriming Indeed, many procedural guides include a step of tapping aportion of the patient line when the line does not appear to be primingproperly. That tapping is meant to dislodge any air bubbles that aretrapped in the fluid line.

A third problem that occurs relatively often in priming is that thepatient forgets to remove the clamp on the patient line prior to primingthat line. That clamped line will not allow the line to prime properly.An alarm is needed to inform the patient specifically that the patientneeds to remove the clamp from the patient line before proceeding withthe remainder of therapy. Fourth, if vented tip protectors are providedat the end of the patient line, the vented tip protectors may not ventproperly and impede priming. An alarm is again needed to inform thepatient that the line has not primed properly. Fifth, cost is always afactor. Besides providing a priming apparatus and method that overcomesthe above problems, it is also desirable to use existing components toperform the priming, if possible, to avoid having to add additionalcomponents and additional costs.

Another concern for medical fluid systems and in particular automatedperitoneal dialysis (“APD”) systems is ensuring that solution bags areplaced at a height relative to the machine that is suitable for themachine to operate within designated parameters. The height of solutionbags, such as dialysate bags, lactate bags and/or dextrose bags, needsto be monitored to ensure that the proper amount of fluid will be pumpedto the patient during therapy and that the correct amount and proportionof additives are infused. Two patents discussing bag positiondetermination are U.S. Pat. Nos. 6,497,676 and 6,503,062.

SUMMARY

The present invention in one primary embodiment performs an integritytest on both the cassette sheeting and the molded cassette features of adisposable cassette. The methodology of the invention is applicable tomany cassette based pumping and liquid distribution systems and isparticularly suited for dialysis treatment, such as automated peritonealdialysis. The steps of the integrity test are performed almostexclusively before solution bags, such as peritoneal dialysis solutionbags, are connected to a dialysis therapy machine, such as a peritonealdialysis machine. Such a test is advantageous because if an integrityproblem arises, the patient only has to discard the disposable cassetteand associated tubing, not the solution. Also, because fluid is notconnected to the machine to perform the test, there is no opportunityfor fluid, due to a leak, to be sucked into the machine's pneumatics,potentially causing malfunction.

The dry testing of the present invention is performed with all fluidlines capped except for the drain line, which is covered with a tipprotector and/or membrane that allows air but not liquid to escape.Because the lines remain capped, they are not connected to the solutionbags. Consequently, no solution bags become contaminated if the cassettehas a leak.

The testing steps are able to be performed with capped lines for anumber of reasons. In some steps, the tip protectors, or caps, connectedto all lines except the drain line are left in place because thecassette sheeting and fluid pathways are tested with valves in the openposition rather than the closed position. When the valves are open, allof the fluid channels in the cassette are in direct communication withboth pump chambers and the drain line, which has a bacteria retentivetip protector that allows air to pass through it. Air from a failed testcan therefore pass through the drain line from cassette, changing thepressure in the system so that a leak can be detected.

In other test steps, the tip protectors can be left in place because onepart of the system is pressurized, while the other is evacuated. Airleaking from the positively pressurized part of the cassette leaks tothe evacuated part and is readily detectable as is air escaping from orleaking into the cassette. Further, because air flows more readily thandoes water or solution through a leak, the air test is more expedientand sensitive than a fluid based test, increasing accuracy andrepeatability and decreasing test time.

The present invention in another primary embodiment provides anapparatus and method for priming a medical fluid delivery system. Thepriming method and apparatus is described herein for an automatedperitoneal dialysis machine, however, the test is applicable to anyfluid delivery system, which requires the purging of air for safety oroperational reasons. The method and apparatus operates with a systemhaving a fluid container or fluid bag, at least one fluid pump and atleast one tubing line, such as a patient line extending from that fluidpump. In a first step of the priming method, valves surrounding thefluid pump are configured so that fluid flows via gravity or via thepump into the pump chamber and fills such pump chamber but does not exitthe chamber. In a second step, the valves are switched so that the fluidin the supply bag is no longer able to fill the pump chambers, and sothat the pump chambers can be pressurized and thereby pump the fluidfrom the pump chambers downstream and partially into the patient line.The machine processor is configured to expect a pressure drop in thepump chamber when the pump chamber expels fluid therefrom. If suchpressure drop is not seen, the patient has likely forgotten to removethe clamp in the patient line and an error message is generated. In afinal step, the valves surrounding the pump are opened so that fluidfrom the container or bag can continue to flow through and prime thepatient line until fluid reaches the end of the patient line, which ispositioned at the same elevational height as the top of the fluid in thefluid container.

As indicated above, if the patient line is inadvertently clamped duringpriming, the pressure in the pump chamber during the pushing step wouldnot fall to an expected level, prompting a suitable alarm. Further, theinitial pushing of fluid through the proximal part of the patient line,nearer to the cassette, in many instances will overcome the resistanceto fluid flow caused by air trapped in that portion of the line, andallow priming to thereafter take place in a proper manner.

Another primary aspect of the present invention is an apparatus andmethod for determining the vertical position or head height of one ormore solution bags as well as a drain bag. The method and apparatus useatmospheric pressure to establish a zero position relative to thetherapy machine, such as an APD machine. The bag height determinationcan determine whether a solution bag is in the proper position toachieve a desired pumped flowrate, whether the solution bag is properlylocated on a heater plate, whether the relative position between two ormore bags is proper, whether the drain bag is located in a properposition or whether one or more of the bags is empty, etc.

It is therefore an advantage of the present invention to provide anintegrity test that consumes less time than previous practices.

It is another advantage of the present invention to provide an integritytest that is more effective at detecting leaks than previous practices.

It is a further advantage of the present invention to provide anintegrity test that is more convenient for the patient if a leak isdetected.

It is another advantage of the present invention to provide an integritytest that minimizes the supplies that must be discarded if a leak isdetected.

It is yet another advantage of the present invention to provide anintegrity test that is immune to failure of other machine components,such as a flow line occluder.

It is still another advantage of the present invention to provide anintegrity test that does not require warm solution.

It is still a further advantage of the present invention to provide anintegrity test from which it is possible for a user to distinguishbetween a failure of the disposable set and a leak in the pneumaticsystem of the machine or cycler.

Moreover, it is an advantage of the present invention to eliminate falsetriggering due to cold solution used in integrity testing.

Still further, it is an advantage of the present invention to provide apriming method and apparatus that operates to automatically dislodge airpockets located initially in the priming line, which would otherwisetend to slow or completely stop priming.

Yet another advantage of the present invention is to provide a primingmethod and apparatus that detects when the patient or operator hasinadvertently left a clamp on the priming line, so that the therapymachine can generate a suitable alarm.

Further still, an advantage of the present invention is to be able todetermine the elevational location and head height of one or moresolution and drain bags.

Additional features and advantages of the present invention aredescribed in, and will be apparent from, the following DetailedDescription of the Invention and the figures.

BRIEF DESCRIPTION OF THE FIGURES

FIGS. 1 to 4 are opposite views of a cassette showing different areas ofthe cassette that are integrity tested during a known integrity test.

FIG. 5 is a plan view of one embodiment of a disposable set operablewith the integrity test of the present invention.

FIG. 6 is a perspective view of one embodiment of a machine that canaccept the cassette of the disposable set shown in FIG. 5.

FIG. 7 is a perspective view of the cassette of the disposable set shownin FIG. 5, wherein flexible membranes of the cassette are exploded toshow various inner components of the cassette.

FIG. 8 is a portion of a cross section taken along line VIII-VIII inFIG. 7.

FIG. 9 is a schematic view of one embodiment of a pneumatic operatingsystem for the machine and cassette shown in FIG. 6.

FIGS. 10 to 15 are elevation views of opposite sides of the cassetteshown in FIG. 5 illustrating the different components or areas of thecassette that are integrity tested in the various steps of oneembodiment of the integrity test of the present invention.

FIG. 16 is a schematic illustration of an alternative medical fluidmachine that employs mechanical positive pressure actuation versuspneumatic pressure.

FIGS. 17 to 22 are schematic views illustrating one apparatus and methodof the present invention for priming a medical fluid system.

FIGS. 23 and 24 are schematic views illustrating a method and apparatusof the present invention that evaluates solution and drain bag headheights.

DETAILED DESCRIPTION

One primary aspect of the present invention is an improved leakdetection system for any type of cassette-based medical fluid therapythat exerts mechanical or pneumatic positive or negative pressure on adisposable fluid cassette. Another primary aspect of the presentinvention is an improved priming technique for a medical fluid therapymachine, such as an automated peritoneal dialysis (“APD”) system. WhileAPD is one preferred use for the present invention, any cassette-basedmedical fluid system or system using a sterile, disposable fluidcartridge can employ the apparatuses and methods of the presentinvention. A further primary aspect of the present invention is toprovide an apparatus and method for determining the head weight of thesolution.

Improved Cassette-Based Leak Test

The following method is a “dry” method, which is more sensitive to leaksand other defects when compared to fluid based integrity testing. Themethod also eliminates some problems associated with older tests, suchas having to discard solution bags or potentially harming the mechanicalcomponents of the machine upon a leak.

Referring now to the figures and in particular to FIGS. 5 to 9, FIG. 5illustrates a disposable set 50 that includes a disposable cassette 100as well as a set of tubes. As shown in the exploded segment 52, thetubing set includes a heater line 54, drain line 56, first proportioningline 58, day/first bag line 60, second proportioning line 62, last fillline 64 and patient line 66. Each of those lines is used with theHomeChoice® machine in one embodiment. It should be appreciated howeverthat other lines associated with other dialysis or medical fluid systemscan be used alternatively with the present invention. Automatedperitoneal dialysis (“APD”) machines, dialysis machines generally ormedical fluid machines besides dialysis machines are collectivelyreferred to herein as medical fluid machine 150, which is shown in FIG.6. More or less lines may also be used without departing from the scopeof the invention.

Each of the lines 54 to 66 terminates at a first end at cassette 100 andat a second end at an organizer 42. In operation, machine 150 holdsorganizer 42 initially at a height that enables a gravity prime to fillfluid at least substantially to the end of at least some of the lines 54to 66 without filling fluid past connectors located at the end of theselines. Priming is discussed in more detail below.

FIG. 6 illustrates that the cassette 100 and tubes 54 to 66 of set 50are loaded vertically in one embodiment into machine 150 and held firmlyin place between door gasket 152 and diaphragm 154. Door gasket 152 isattached to door 156, which swings open and closed to removably lockcassette 100 in place. Diaphragm 154 provides an interface between thevalve and pump actuators, located inside machine 150 behind diaphragm154, and the valve and pump fluid receiving chambers located in cassette100.

FIG. 7 is a perspective view of cassette 100 showing that the cassette100 includes a housing 102, which is sealed on both sides by flexiblemembranes 104 and 106. The housing defines a plurality of pump chambersP1 and P2, valves V1 to V10 (which are located on the opposite side ofhousing 102 from the side shown in FIG. 7), a plurality of flow paths F1to F9 and a plurality of ports 108 that extend through an interiordivider 110 that divides housing 102 and cassette 100 into two separatefluid flow manifolds.

FIG. 8 illustrates a cross-section taken through line VIII-VIII shown inFIG. 7. The cross-section shows membrane 106, divider 110 and a port 108described above. Additionally, external valve chamber walls 112 andinternal valve chamber wall 114 are illustrated, which cooperate toproduce one of the valves V1 to V10 on one side of divider 110 ofcassette 100. Further, internal chamber wall 114 cooperates with a back116 (which can also be a flexible membrane) to create various ones ofthe flow paths F1 to F11 on the other side of divider 110 of cassette100. Flexible membrane 106 seals to external chamber walls 112 and uponapplication of a force f to internal chamber walls 114 (to close a fluidconnection between a first one of the paths F1 to F11 and a second oneof those paths). Upon the release of force f or the application of avacuum or negative force to membrane 106, membrane 106 is pulled awayfrom internal wall 114, reestablishing the communication between thefluid paths.

FIG. 9 illustrates a schematic view of a pneumatic control system 10 fora dialysis machine, such as an automated peritoneal dialysis machine isillustrated. FIG. 9 is a schematic of the pneumatic control systememployed in the HomeChoice® Automated Peritoneal Dialysis system and isuseful for describing the operation of the present invention. It shouldbe appreciated however that the teachings of the present invention arenot limited to the HomeChoice® machine nor to only those machines havingthe same or analogous components. Instead, the present inventiondescribes a test and methodology that is applicable to many differentmedical fluid systems.

In a set-up portion of the integrity test of the present invention,disposable cassette 100 is loaded into dialysis machine 150. To do so,an air pump (not illustrated) is turned on. That air pump communicateswith various pneumatic components illustrated in FIG. 9, includingemergency vent valve A5, occluder valve C6, and actuators C0, C1, C2,C3, C4, D1, D2, D3, D4 and D5 for the fluid valves, which causes anoccluder 158 (see also FIG. 6) to retract to enable the disposable set50 and cassette 100 to be loaded into machine 150. Once the set 50 hasbeen loaded, emergency vent valve A5 is closed, so that high positivebladder 128 can be inflated, which seals cassette 100 between the door156 and diaphragm 154, while maintaining the occluder 158 in an openposition (FIG. 6). The remainder of the test is illustrated by FIGS. 10to 14.

Referring now to FIG. 10, a first step of the test tests the pumpchambers P1 and P2 using positive pressure and tests valves V1 to V10using negative pressure. In particular, the cassette sheeting ofcassette 100 over pump chambers P1 and P2 is pressurized to +5 psigusing the low positive pressure tank 220 and valves A3 and B1 shown inFIG. 9. A −5 psig vacuum is pulled on the cassette sheeting of cassette100 over the fluid valves V1 to V10 using negative tank 214 and valvesA0 and B4 shown in FIG. 1.

Simultaneous pressure decay tests are then conducted on the: (i) airvolume in the low positive tank 220 and pump chambers P1 and P2; and(ii) the air volume in the negative tank 214 and fluid valves V1 to V10.If the pressure decay in the positive pressure system exceeds, e.g., onepsig, an alarm is sent displaying a pump chamber sheeting damaged erroror code therefore. If the difference in pressure in the negativepressure system exceeds, e.g., one psig, an alarm is sent displaying afluid valve sheeting damaged error or code therefore. Positive pressuretested areas for this first step are shown in double hatch and negativepressure tested areas are shown in single hatch in FIG. 10.

Importantly, test step one tests cassette 100 from the outside. That is,the pressure is applied to the outside of the sheeting over pumpchambers P1 and P2 and negative pressure is applied to the outside ofthe sheeting over valves V1 to V10. As described below, the remainingtest steps apply positive pressure and negative pressure to the sheetingfrom inside the cassette. The designation of the Figures however is thesame, namely, positive pressure tested areas (internal and external) areshown using a double hatch. Negative pressure tested areas (internal andexternal) are shown using a single hatch. The ports 108 tested in eachstep are darkened and labeled either “positive pressure tested” or“negative pressure tested”.

Referring now to FIG. 11, a second step of the test of the presentinvention tests the pump chambers P1 and P2, certain fluid pathways andcertain valves using positive pressure and negative pressure. The secondstep begins by evacuating negative tank 214 to −5 psig and opening valveB4 to fill pump chamber P2 in the cassette with air through open fluidvalve V7. Next, low positive pressure tank 220 is pressurized to +5 psigand valve A3 is opened to empty pump chamber P1 through open fluid valveV10. Fluid valves V7 and V10 are then closed. Occluder valve C6 isde-energized so that occluder 158 closes, pinching/sealing all fluidlines 54 to 66 exiting cassette 100. Valves A3 and B4 are then closed.Actuator valve B1 is opened with fluid valves V4, V6 and V7 open topressurize the air in cassette pump chamber P2 and to test the fluidpathways downstream of V4, V6 and V7 for leakage across the occluder 158and/or across the fluid channels within the cassette. Actuator valve A0is then opened with fluid valves V1, V2 and V9 open to create a vacuumin cassette pump chamber P1 and to test the fluid pathways downstream ofV1, V2 and V9 for leakage across occluder 158 and/or across the fluidchannels within the cassette.

Next, a first set of simultaneous pressure decay/rise tests is conductedon low positive pressure tank 222 and negative pressure tank 214. Thedifference in pressure in both positive pressure tank 220 and negativepressure tank 214 is recorded as well as the final pressure in positivepressure tank 220 and negative pressure tank 214. Valve V3 is opened anda second set of simultaneous pressure decay/rise tests is conducted onlow positive pressure tank 220 and negative pressure tank 214 as thecontents of pump chamber P2 flow freely into pump chamber P1 throughopen valves V1 and V3. If the sum of difference in pressures from thefirst set of pressure decay tests exceeds, for example, two psig, andthe sum of the difference in pressure from the second set of tests isless than one psig, an alarm is issued for a cross-talk leakage error.Positive pressure tested areas for the second step are shown in doublehatch and with ports 108 so marked and negative pressure tested areasare shown in single hatch and with ports 108 so labeled in FIG. 11.

Referring now to FIG. 12, a third step of the test tests the pumpchambers P1 and P2, certain fluid pathways and certain valves usingpositive pressure and negative pressure. The third step begins byevacuating negative pressure tank 214 to −5 psig and opening valve B4 tofill pump chamber P2 in the cassette with air through open fluid valveV7. Low positive pressure tank 220 is then pressurized to +5 psig andvalve A3 is opened to empty pump chamber P1 through open fluid valveV10. Valves V7 and V10 are then closed. Occluder valve C6 isde-energized so that the occluder 158 closes, pinching/sealing all fluidlines exiting cassette 100. Valves A3 and B4 are closed. Pump actuatorvalve B1 is opened with fluid valves V3, V4 and V6 open to pressurizethe air in pump chamber P2 and to test fluid pathways downstream of V3,V4 and V6 for leakage across occluder 158 and/or across the fluidchannels within cassette 100. Pump actuator valve A0 is then opened withfluid valves V2, V9 and V10 open to create a vacuum in pump chamber P1and to test the fluid pathways downstream of V2, V9 and V10 for leakageacross the occluder 158 and/or across the fluid channels within cassette100.

Next, a first set of simultaneous pressure decay/rise tests is conductedon low positive pressure tank 222 and negative pressure tank 214. Thedifference in pressure in both positive tank 220 and negative tank 214is recorded as well as the final pressure in positive pressure tank 220and negative pressure tank 214. Valve V1 is opened and a second set ofsimultaneous pressure decay/rise tests is conducted on low positivepressure tank 220 and negative pressure tank 214 as the contents of pumpchamber P2 flow freely into pump chamber P1 through open valves V1 andV3. If the sum of the difference in pressure from the first set ofpressure decay tests exceeds, for example, 2 psig, and the sum of thedifference in pressure from the second set of tests is less than onepsig, a cross-talk leakage error alarm or code therefore is sent.Positive pressure tested areas for the third step are shown in doublehatch and with ports 108 so marked and negative pressure tested areasare shown in single hatch and with ports 108 so marked in FIG. 12.

Referring now to FIG. 13, a fourth step of the test tests the pumpchambers P1 and P2, certain fluid pathways and certain valves usingpositive pressure and negative pressure. The fourth step begins byevacuating negative pressure tank 214 to −5 psig and opening valve B4 tofill pump chamber P2 in cassette 100 with air through open fluid valveV7. Low positive pressure tank 220 is pressurized to +5 psig and valveA3 is opened to empty pump chamber P1 through open fluid valve V10.Fluid valves V7 and V10 are closed. Occluder valve C6 is de-energized sothat the occluder 158 closes, pinching/sealing fluid lines 54 to 66exiting cassette 100. Valves A3 and B4 are closed. Pump actuator valveB1 is opened with fluid valve V5 open to pressurize the air in pumpchamber P2 and to test the fluid pathways downstream of V5 for leakageacross the occluder 158 and/or across the fluid channels within cassette100. Pump actuator valve A0 is opened with fluid valves V1, V2, V9 andV10 open to create a vacuum in pump chamber P1 and to test the fluidpathways downstream of V1, V2, V9 and V10 for leakage across theoccluder 158 and/or across the fluid channels within the cassette.

Next, a first set of simultaneous pressure decay/rise tests is conductedon low positive pressure tank 222 and negative pressure tank 214. Adifference in pressure in both positive tank 220 and negative tank 214is recorded as well as the final pressure in positive pressure tank 220and negative pressure tank 214. Valve V3 is opened and a second set ofsimultaneous pressure decay/rise tests is conducted on low positivepressure tank 220 and negative pressure tank 214 as the contents of pumpchamber P2 flow freely into pump chamber P1 through open valves V1 andV3. If the sum of the difference in pressure from the first set ofpressure decay tests exceeds, for example, 1.5 psig, and the sum of thedifference in pressure from the second set of tests is less than 0.75psig, a cross talk leakage error alarm or code is sent and displayed.Positive pressure tested areas for the forth step are shown in doublehatch and with ports 108 so marked and negative pressure tested areasare shown in single hatch and with ports so marked 108 in FIG. 13.

Referring now to FIG. 14, a fifth step of the test tests the pumpchambers P1 and P2, certain fluid pathways and certain valves usingpositive pressure and negative pressure. The fifth step begins byevacuating negative pressure tank 214 to −5 psig and opening valve B4 tofill pump chamber P2 in cassette 100 with air through open fluid valveV7. Low positive pressure tank 220 is pressurized to +5 psig and valveA3 is opened to empty pump chamber P1 through open fluid valve V8. Fluidvalves V7 and V10 are closed. Occluder valve C6 is de-energized so thatthe occluder 158 closes, pinching/sealing fluid lines 54 to 66 exitingcassette 100. Valves A3 and B4 are closed. Pump actuator valve B1 isopened with fluid valves V3, V4, V6 and V7 open to pressurize the air inpump chamber P2 and to test the fluid pathways downstream of V3, V4, V6and V7 for leakage across the occluder 158 and/or across the fluidchannels within cassette 100. Pump actuator valve A0 is opened withfluid valve V8 open to create a vacuum in pump chamber P1 and to testthe fluid pathways downstream of V8 for leakage across the occluder 158and/or across the fluid channels within the cassette.

Next, a first set of simultaneous pressure decay/rise tests is conductedon low positive pressure tank 222 and negative pressure tank 214. Adifference in pressure in both positive tank 220 and negative tank 214is recorded as well as the final pressure in positive pressure tank 220and negative pressure tank 214. Valve V1 is opened and a second set ofsimultaneous pressure decay/rise tests is conducted on low positivepressure tank 220 and negative pressure tank 214 as the contents of pumpchamber P2 flow freely into pump chamber P1 through open valves V1 andV3. If the sum of the difference in pressure from the first set ofpressure decay tests exceeds, for example, 1.5 psig, and the sum of thedifference in pressure from the second set of tests is less than 0.75psig, for example, a cross talk leakage error alarm or code is sent anddisplayed. Positive pressure tested areas for the fifth step are shownin double hatch and with ports 108 so marked and negative pressuretested areas are shown in single hatch and with ports 108 so marked inFIG. 14.

In each of test steps two through five of FIGS. 11 to 14 describedabove, pump chamber P2 is filled with air and pump chamber P1 isevacuated before the pressure decay/vacuum rise tests are performed.Those tests are improved when chamber P2 is pressurized aboveatmospheric pressure as opposed to merely maintaining the chamber atatmospheric pressure. For one reason, maintaining chamber P2 at apositive compensates for the slight compressibility of air in thechamber when the test steps are commenced. To pressurize chamber P2, aircan be pushed from chamber P1 to P2 with the occluder 158 closed. WhenP2 is pressurized, occluder 158 is opened, enabling chamber P1 to beevacuated. Pressurized chamber P2 should show very little pressure dropunless a leak in one of the tested pathways is detected.

Referring now to FIG. 15, a sixth step of the test of the presentinvention tests the pump chambers P1 and P2, certain fluid pathways andcertain valve ports 108 using positive pressure. To begin the sixthstep, a −5 psig vacuum is pulled on the cassette sheeting over the twopump chambers P1 and P2 with all fluid valves except for drain valves V7and V10 de-energized (closed), so that pump chambers P1 and P2 fill withair. Valves V7 and V10 are closed and the sheeting over pump chambers P1and P2 of cassette 100 is pressurized to +5 psig using low positive tank220 and valves A3 and B1. A first pressure decay test is then conductedon the pump chambers P1 and P2, fluid flow paths F6, F7, F8 and F9 andthe darkened fluid ports 108 so marked within cassette 100 by monitoringthe pressure in the low positive tank 220. If the difference in pressurein the low positive tank 220 exceeds, e.g., one psig, an alarm is sentdisplaying a fluid valve leaking error or code therefore.

Occluder valve C6 is de-energized so that occluder 158 closes,pinching/sealing all fluid lines 54 to 66 exiting cassette 100. All ofvalves V1 through V10 except for V5 and V8 are opened and a secondpressure decay test is conducted by monitoring the pressure in lowpositive tank 220. If the difference in pressure in the low positivetank 220 exceeds, e.g., one psig, the sixth series of tests must berepeated. If the difference in pressure in the low positive tank 220exceeds, e.g., one psig a second time, a an alarm is sent displayingoccluder failed. Finally, the occluder is opened and a third pressuredecay test is conducted by monitoring the pressure in low positive tank220. Test step six verifies that tests one and two have not failed ifthe difference in pressure exceeds, e.g., one psig. Positive pressuretested areas for the sixth step are shown in double hatch and with ports108 so marked in FIG. 15.

The previous six test steps complete one embodiment of the dry integritytest of the present invention. Viewing the outcome of steps 1 to 4 ofthe prior art test in FIGS. 1 to 4, it should be appreciated that step1, shown in FIG. 10 of the dry disposable integrity test of the presentinvention, tests the equivalent components of all four steps of theoriginal dry integrity test.

Importantly, test steps two to six test the cassette from the inside.That is, positive pressure is applied inside the cassette to the insideof the cassette sheeting and negative pressure is applied inside thecassette to the inside of the cassette sheeting. The positive andnegative pressure applied inside the cassette to the inside of thecassette sheeting is created by initially applying pressure (positive ornegative) to the outside of the cassette and switching the valves tocreate the desired pressure distribution inside the cassette asdescribed above.

The first five of the test steps (FIGS. 10 to 14) can be performed withthe tip protectors placed on lines 54 through 66 and with the clampsclosed on all of the lines except for drain line 56. The tip protectors,shown figuratively as caps 118 on the respective ports of cassette 100,are actually at the ends of tubes 54, 58, 60, 62, 64 and 66. The drainline 56 has a bacteria retentive tip protector that passes to atmosphereair that leaks through the membranes 104 and 106 (FIGS. 7 and 8) or fromhousing 102, lowering the pressure in the system so that a leak can bedetected. The tip protectors are removed when solution bags areconnected to the tubes prior to test step six in the series of six teststeps. As seen in the prior steps 2 to 4 of FIGS. 2 to 4, all tipprotectors have to be removed for those test steps. In the prior arttherefore, when a cassette fails during any of the tests illustratedFIGS. 2 to 4, non-sterile air is introduced into the solution bags,causing the solution bags and the cassette to be discarded.

Test steps two through five of the present invention (FIGS. 11 to 14,respectively) test, using air within cassette 100, the same areas of thecassette as does the prior art wet leak test described above. Becausesteps (i) through (v) of the prior art wet leak test require fluid,solution bags must be attached to obtain such fluid. The presentinvention eliminates that necessity.

Test step one of the present invention is able to leave the tipprotectors connected to all lines except the drain line because thevalves are tested in the open position rather than the closed position.When valves V1 to V10 are open, all of the fluid channels F1 to F11 incassette 100 are in direct communication with both pump chambers P1 andP2 and the drain line. The drain line has a bacteria retentive tipprotector that allows air to pass through it, e.g., is fitted with ahydrophobic membrane. Air from a failed test can therefore pass throughthe drain line from cassette 100, changing the pressure in the system sothat a leak can be detected.

Test steps two through five of the disposable integrity test of thepresent invention are able to leave the tip protectors in place becauseone part of the system is pressurized while the other is evacuated. Airleaking from the positively pressurized part of cassette 100 to theevacuated part is readily detectable as is air escaping from or leakinginto cassette 100. Because air flows more readily than does water orsolution through a leak, the air test is more expedient and sensitivethan a fluid based test, increasing accuracy and repeatability anddecreasing test time.

Test steps two through five of the present invention include a redundantpressure decay test that verifies the results of the first pressuredecay test. All four test steps two through five look for leaking flowfrom a pressurized section of cassette 100 to an evacuated section ofthe cassette 100. If a leak arises between the two sections of thecassette, the pressure in the two sections should tend towardsequilibrium when air flows from the high pressure section to theevacuated section. The redundant test opens valves between the positiveand negative sections at the completion of the first pressure decay testto verify that there is a larger pressure change if no leaks exist or aminimal pressure change if a leaks exists.

A failure of occluder 158 to properly crimp tubing lines 54 to 66 doesnot materially affect the results for test steps two to five because thetip protectors are in place and would otherwise seal all of the linesthat are being tested. Additionally, the users/patients are instructedto close the line clamps on all but the drain line when loading set 50into machine 150. Test step six, which tests the cassette valves V1through V10 and the occluder 158, can be conducted dry or wet since thesolution bags have been connected. The dry test would have to bepressure based, whereas the fluid test could be either pressure orvolume based.

The user can clamp the drain line on the disposable set when instructedto do so after an integrity test failure when using the method of thepresent invention and run the disposable integrity tests again. If thetests do not show a failure a second time (for many of the failuremodes), the disposable set can be held responsible for the leak and notthe machine 150, e.g., the machine's pneumatic system and/orcassette/machine interface. That feature is useful when a patient seekstroubleshooting assistance. Determining that the machine 150 is workingproperly and that the cassette 100 is causing the failure precludesswapping a patient's machine needlessly after an integrity failurebecause of uncertainty about whether the cassette 100 or machine 150 isresponsible for the test failure. Conversely, if the tests show afailure a second time, the machine 150 and/or the cassette/machineinterface can be held responsible for the leak.

While cassette 100 is illustrated with pump chambers P1 and P2, valvechambers V1 to V10, associated ports 108, and fluid paths F1 to F11, itshould be appreciated that the method of the invention is equallyapplicable to cassettes and actuating systems that have different pumpand valve geometries than the ones shown as well as additional features,such as heaters, pressure sensors, temperature sensors, concentrationsensors, blood detectors, filters, air separators, bubble detectors,etc. The cassettes can be rigid with a single side of sheeting, be rigidwith dual sided sheeting, have dual sheets forming fluid pathways, havea rigid portion connected to a flexible portion, etc. The cassettes areuseable in any medical fluid delivery application, such as peritonealdialysis, hemodialysis, hemofiltration, hemodiafiltration, continuousrenal replacement therapy, medication delivery, plasma pherisis, etc.,and any combination thereof.

FIG. 16 shows one alternative embodiment of the present invention viasystem 200, wherein the pneumatic source of positive pressure used aboveis replaced by a mechanical actuator 202 that pushes a flexible membranefilm 203. Film 203 is attached to a cassette 210 with sheeting 204 onone side of thereof. System 200 uses a vacuum to force the membrane 203to follow a piston head 206 when head 206 retracts from or moves towardcassette 210. While no external source of positive pressure is provided,air can be drawn into pumping chamber 208, while fluid valve 212 isclosed and actuator 202 and head 206 are moved forward to generate aninternal pressure that is used to perform the disposable integrity testsdescribed herein. A pressure sensor 214 is provided in one embodiment toperform the pressure decay tests. The position of actuator 202 and head206 can also be used to perform a leak test by applying a constantforce. The actuator and head should remain stationary when a constantforce is applied if no leak is present. Forward motion would indicatethat there is a leak in the system being tested.

Appendix A shows data from step one of the integrity test of the presentdisclosure. Appendix B also shows data from step one of the integritytest of the present disclosure. In Appendix B, the bolded, larger fontsize data shows when defects were detected. It is noteworthy that forfifty different cassettes tested and known to be defective, all fiftydefects were detected. When the drain line was clamped after thesoftware instructed the operator to do so, forty-seven of the fiftytests no longer failed indicating that the leak was in the cassette andnot the therapy machine. The other three of the fifty clamped tests wereinconclusive. Those three are marked in bolded italics. It is alsonoteworthy that one cassette appears to have two defects and ishighlighted in bold italics as well.

For the test, ten defects were created in the pump chamber sheeting andforty defects were created in the valve sheeting. All pump chamber testswere run with positive pressure and all valve sheeting tests were runwith negative pressure. The defects were punctures and slits made by a0.035 inch (0.89 mm) outside diameter hot needle or an Exacto knife witha stop positioned to create consistent slits of 0.125 inch (3.2 mm)

Appendix C shows data from the integrity test step two of the presentdisclosure. The positive pressures represent pressures inside pumpchamber P2, as measured by pressure sensors monitoring positive tank 220(FIG. 9). The negative pressures are for pressures inside pump chamberP1, as measured by the pressure sensors monitoring negative tank 214(FIG. 9). Cassettes predisposed with a number of defects were tested aswell as some cassettes without known defects. Some of the defects werenot detected by test step two. Test steps three, four and five didhowever reveal the defects that test step two did not.

Improved Priming Method and Apparatus

Turning to the priming method and apparatus of the present invention,the method and apparatus are advantageous in a number of respects.First, the method employs the pumps of the medical fluid machine 150shown above in FIG. 6 to pump priming fluid for an initial portion ofthe prime to dislodge air bubbles that typically become trapped, forexample, in the patient line 66, near cassette 100. Second, the methoduses software contained within the controller of machine 150 thatexpects to see a particular pressure drop when the medical fluid pump(or pumps) pushes the initial priming fluid. If the expected pressuredrop is not seen, machine 150 assumes there is a clamp on the priming orpatient line, responds accordingly and sends a suitable error message orcode.

Referring now to FIG. 17, an initial schematic of an apparatus 250 forperforming the priming method of the present invention is shown. Theapparatus includes a supply bag 252 filled with a volume of fluid 254. Aline from solution bag 252 to pumps P1 and P2 is provided. In mostinstances, that line is the heater bag line 54 shown in FIGS. 5 and 17,which enters cassette 100 that houses pump chambers P1 and P2. Valves256 and 258 selectably allow fluid 254 to pass via line 54 to pumpchambers P1 and P2, respectively. A priming line is provided from pumpchambers P1 to P2 to a distal end of the line, which is provided with avented distal end connector 260. Normally, the primed line is thepatient line shown as line 66 in FIGS. 5 and 17. It should beappreciated, however, that the priming line may be a different line thanthe patient line. Moreover, the priming apparatus 250 and associatedmethod is applicable to systems that prime multiple lines sequentiallyor simultaneously.

Connector 260 as illustrated is positioned in organizer 42 discussedabove in connection with FIG. 5. The positioning of connector 260 is setso that the prime stops at a desired point at the beginning of or in theinterior of connector 260. That level as shown by line 262 is the samelevel as the height of fluid 254 in container 252. Valves 266 to 268 areprovided between pumps P1 and P2 and connector 260 to selectively allowfluid to enter patient line or priming line 66.

The first step of the priming method shown in FIG. 17 is to close valves266 and 268 (black) and open valves 256 and 258 (white). Such valvearrangement enables fluid 254 to gravity feed or be drawn in by pumps P1and P2 (the −1.5 psig shown in FIG. 17 symbolizes the suction beingapplied to the flexible pump film as fluid is drawn into the pumpchamber) from container 252 and fill pump chambers P1 and P2. Becausevalves 266 and 268 are closed, no fluid enters priming line 66.

FIG. 18 illustrates a second step of the priming method of the presentinvention. In FIG. 18, valves 256 and 258 are closed (black), so that noadditional fluid can flow via heater bag line 54 from container 252 topump chambers P1 and P2. Next, a 1.0 psig pressure is applied to theflexible pump film, pressing the film against the fluid in pump chambersP1 and P2. Valves 266 and 268 are then opened (white) so that fluidcommunication exists between pump chambers P1 and P2, priming or patientline 66 and connector 260.

FIG. 19 illustrates that after pressurizing the pump chambers P1 and P2,fluid flows from those chambers through an initial portion of patient orpriming line 66. The pressure inside pump chambers P1 and P2 fallsaccordingly, e.g., to about 0.1 psig, as this fluid is displaced fromthe pump chambers and the volume of air pushing against the pump filmexpands. The fluid pumped from chambers P1 and P2 is not meant to extendall the way to connector 260, rather, the pumped fluid is intended toflow through any trapped air at the proximal end of patient line 66, sothat such air is not an impediment to priming Therefore, the fluidvolume drawn into pump chambers P1 and P2 should be less than the volumeinside patient line 66 extending from cassette 100 to connector 260.

The volume of liquid that does fill patient line 66 via the pump strokeof chambers P1 and P2 does, however, push some air through ventedconnector 260, leaving the line partially filled with solution andpartially filled with air, wherein the air is collected at the distalend and the solution resides at the proximal end of line 66. This methodof dislodgement works regardless of how many extensions are added topatient line 66. Older priming sequences had varied results dependingupon whether a standard or non-standard length of patient line was used.The present method is independent of patient line length and can be usedwith a heater bag containing as little as 1000 ml of solution as seen inTable 1.

TABLE 1 Patient Line Priming Height 1000 ml 6000 ml 1000 ml heater bagheater bag heater volume volume bag volume Average Primed Height AboveTable Set with no patient extension line 7.17 7.8 6.28 Set with 1patient extension line 6.8 7.95 6.34 Set with 2 patient extension lines6.5 7.88 6.23 Standard Deviation in Primed Height Above Table Set withno patient extension line 0.52 0.16 0.27 Set with 1 patient extensionline 1.35 0.16 0.11 Set with 2 patient extension lines 0.5 0.13 0.23

FIGS. 20 and 21 illustrate the final step in the priming methodassociated with apparatus 250. Here, inlet valves 256 and 258 areopened, while outlet valves 266 and 268 are left open.

In FIG. 20, any fluid in pump chambers P1 and P2 not pumped in FIG. 19is allowed to flow via gravity from such pump chambers into patient line66. Additionally, fluid 254 is enabled to gravity flow from container252 to complete the patient line prime. In FIG. 20, the pressure inchambers P1 and P2 can drop to near zero psig as any remaining pressurefrom the pump stroke in FIG. 19 is dissipated. FIG. 21 shows that thepatient or priming line 66 is fully primed, with the level of fluid 254reaching the elevational height 262 of the fluid 254 remaining in bag252. The level of fluid inside pump chambers P1 and P2 will also reachsome equilibrium which may be at a slight positive pressure within thosechambers. That is, the pressure in the pump chamber will equalize withthe head pressure of patient line 66 and fill bag 252.

If the patient line 66 is inadvertently clamped during priming, thepressure in pump chambers P1 and P2 in the step illustrated by FIG. 19does not fall below an expected level, e.g., from the one psig shown inFIGS. 18 to 0.1 psig shown in FIG. 19. The pressure instead remains at ahigher level, such as 0.5 psig. The controller inside machine 150 sensesthat discrepancy and prompts the patient via a visual, audio oraudiovisual message to unclamp the patient or priming line 66.

FIG. 22 illustrates another advantage of the priming method of thepresent invention. A mixture of air and fluid can sometimes appear inthe proximal part of the patient line 66, near cassette 100, at thebeginning of prime. The mixture is usually near the cassette 100 becausefluid may have entered into the line due to procedural errors during thesetup procedure. For example, the patient may improperly connect thesolution bags and open the clamps when the set is loaded. The mixture ofair and fluid 254 can sometimes slow and sometimes prevent properpriming. The pressurized assist beginning in FIG. 18 and ending in FIG.19 of patient line 66 will typically dislodge or overcome the problemscaused by the air/fluid mixture, enabling proper priming.

FIG. 16 discussed above shows one alternative embodiment of the primingmethod of present invention, wherein system 200 replaces pneumatic pumpsP1 and P2 in FIGS. 17 through 21. The pneumatic source of positivepressure used in FIG. 19 is replaced by a mechanical actuator 202, whichpushes on a flexible membrane film 203, which in turn is attached to acassette 210 having sheeting 204 on one side of thereof. System 200 usesa vacuum to force membrane 203 to follow a piston head 206 when head 206retracts and moves toward cassette 210, drawing fluid into pumpingchamber 208 when fluid valve 212 is open. Actuator 202 and head 206 aremoved forward when another fluid valve (not shown) is opened, pushingfluid down the patient line. A pressure sensor 214 detects a pressurerise if the patient line is clamped. The position of actuator 202 andhead 206 can be used to determine when to open valve 212 so that gravitycan complete the priming of the patient line.

Appendix D shows data from the priming method of the present invention.Additionally, the data in Appendix E, Tables 3 and 4, was obtained froma software program that opened valves 256 and 258 when the pressure inpump chambers P1 and P2 fell below 0.2 psig. If the pressure did notfall to below 0.2 psig, the pressure was recorded and a message waslogged that stated, “Timeout before PosP reached 0.20 psig”. A number ofnormal primes were performed as well as a number of primes wherein thepatient line was clamped near the patient connector at the distal end ofthe line.

Solution Bag Head Height Determination

Dialysis, such as peritoneal dialysis or hemodialysis or other renaltherapies such as hemofiltration or hemodiafiltration can performedusing multiple solution bags, such as dialysate bags, lactate bagsand/or dextrose bags. In such a case, it is advantageous to determinethat the required solution bags are: (i) present and (ii) located at avertical height suitable to enable the particular therapy to beperformed, for example, an automated peritoneal dialysis performed by amachine. Such determinations should be made at the beginning of therapy,e.g., during the priming and cassette integrity tests, so that themachine can alert the patient of any problems before treatment beginsand/or before the patient falls asleep.

Referring now to FIGS. 23 and 24, a system 300 illustrating oneembodiment for determining solution bag head height is illustrated.System 300 of FIG. 23 includes solution bags 302 and 304, which areconnected fluidly to pump chambers 306 and 308 via fluid lines 310 and312, respectively. Pump chambers 306 and 308 house flexible diaphragms314 and 316, respectively. Dialysate or therapy fluid can flow from pumpchambers 306 and 308 when fluid valves 318 and 320 are opened, throughfluid pathway 322, to drain bag 324.

System 300 includes valves 326 and 328 connected fluidly to chamber 306and valves 330 and 332 connected fluidly to chamber 308. Air/vacuumchambers 338 and 340 are placed between valves 326 and 328 and 330 and332, respectively. Differential pressure sensors 334 and 336 sensedifferential pressure within chambers 338 and 340, respectively. Itshould be appreciated that if valves 326, 328, 330 and 332 are open,while pump chambers 306 and 308 are empty, differential pressure sensor334 (placed between valves 326 and 328) and differential pressure sensor336 (placed between valves 330 and 332) and are zeroed because thepressures in air/vacuum chambers 338 and 340 are equal to atmosphericpressure.

As seen in FIG. 24, when valves 318, 320, 328 and 332 are closed andfluid valves 326, 330, 342 and 344 are opened, fluid from solution bags302 and 304 flows vertically down fluid pathways 310 and 312,respectively, into pump chambers 306 and 308. Respective flexiblediaphragms 314 and 316 move when fluid flows into pump chambers 306 and308, causing a pressure rise in the air trapped in air/vacuum chambers338 and 340. Fluid flows into chambers 306 and 308, through open valves342 and 344, until the pressure in respective air/vacuum chambers 338and 340, as measured by pressure sensors 334 and 336, is equal to thepressure exerted by the solution (approximately water for purposes ofdensity) in columns that are equal in height to vertical distances Y1and Y2.

If the pressure equivalent to that exerted by columns of solution ofheights Y1 and Y2 is within a predetermined operating parameter for themedical fluid therapy system 300 (e.g., an APD system), the therapy isallowed to continue. If not, a suitable alarm is posted informing thepatient or operator that one or both solution bags 302 or 304 ispositioned outside the operating parameters of system 300.

A pressure difference caused by differences in the vertical positions(pressure head heights) of solution bags 302 and 304 also has to bewithin set limits for system 300 to operate within specification in oneembodiment. An inlet side of a pump subjected to a negative head heightresults in less fluid being pumped for each stroke of chambers 306 and308, as compared to strokes made when positive head height pressure isseen on the inlet side of a pump. Therefore when equal volumes ofdifferent solutions are being pumped by chambers 306 and 308 and mixedat a desired ratio, e.g., 1:1, it is advantageous for the verticalpositions and corresponding pressure head heights of the two solutionsto be the same or substantially the same.

The previous description of system 300 in FIGS. 23 and 24 illustrateshow sensors 334 and 336 can be zeroed and then used to test solution bagheight in the context of a filling sequence, i.e., pump chambers 306 and308 moving from empty towards full. It should be appreciated thatconversely, sensors 334 and 336 can be zeroed and then used to testdrain bag height in the context of a drain sequence, i.e., pump chambers306 and 308 moving full or partially full towards empty.

In the drain test, pump chambers 306 and 308 are first filled with fluidfrom solution bags 302 and 304, respectively, by opening valves 342 and344, so that therapy fluid flows through fluid pathways 310 and 312,respectively, and into pump chambers 306 and 308 as shown in FIG. 24.Valves 326, 328, 330 and 332 are then opened, allowing the pressure inair/vacuum chambers 334 and 336 to be zeroed with respect to atmosphericpressure and enabling the differential pressure sensor readings ofsensors 334 and 336 to be set or reset to zero.

Valves 342, 344, 328 and 332 are then closed and valves 318, 320, 326and 330 are opened. Fluid flows then from pump chambers 306 and 308,through fluid pathway 322, to drain bag 324. Diaphragms 314 and 316within pump chambers 306 and 308 move accordingly, creating vacuumsrespectively inside air/vacuum chambers 338 and 340. Fluid flow stopswhen the vacuum in air/vacuum chambers 338 and 340, measured by pressuresensors 334 and 336, respectively, is equal to a column of solution(negative pressure head height) of height Y3 shown in FIG. 23.

The drain test ensures that the drain bag/drain line discharge islocated below pump chambers 306 and 308, so that no backflow occurs dueto gravity. The drain test also ensures that the drain is not locatedtoo far below the pumps and valves, wherein the location causes anadverse effect on the operation of the valves. If the pressureequivalent to a column of solution of height Y3 is within apredetermined operating parameter for the medical fluid therapy system300, the therapy is allowed to continue. If not, a suitable alarm isposted informing the patient or operator that the drain bag 324 ispositioned outside the operating parameters of system 300.

It should be understood that various changes and modifications to thepresently preferred embodiments described herein will be apparent tothose skilled in the art. Such changes and modifications can be madewithout departing from the spirit and scope of the present invention andwithout diminishing its intended advantages. It is intended that suchchanges and modifications be covered by the appended claims.

The invention is claimed as follows:
 1. A method for operating adialysis cassette including a flexible membrane that covers a pumpchamber, the method comprising: allowing a source of fluid to fluidlycommunicate with the pump chamber of the dialysis cassette; filling thepump chamber with the fluid from the source; mechanically extending theflexible membrane into the pump chamber with a piston head to expel thefluid from the pump chamber through a flow path; and directly sensing apressure of the fluid flowing through the flow path at a location of thedialysis cassette adjacent to the pump chamber and using the sensedpressure to perform a test prior to delivering fluid to a patient. 2.The dialysis cassette operating method of claim 1, wherein the testincludes determining that a line occlusion has occurred based on thesensed pressure.
 3. The dialysis cassette operating method of claim 1,which includes pulling a vacuum on the flexible membrane, opening themembrane within the pump chamber to fill the pump chamber with thefluid.
 4. The dialysis cassette operating method of claim 1, whereindirectly sensing the pressure includes directly sensing the pressure ofthe fluid flowing through the flow path at a location of the dialysiscassette between the pump chamber and a valve actuation position of theflow path.
 5. The dialysis cassette operating method of claim 1, whereindirectly sensing the pressure includes contacting the flexible membranewith a pressure sensor.
 6. A method for operating a dialysis cassetteincluding a flexible membrane that covers a pump chamber, the methodcomprising: allowing a source of fluid to fluidly communicate with thepump chamber of the dialysis cassette; filling the pump chamber with thefluid from the source; pushing the flexible membrane into the pumpchamber to expel the fluid from the pump chamber through a flow path;directly sensing a pressure of the fluid flowing through the flow pathat a location of the dialysis cassette adjacent to the pump chamber; anddetermining that a line occlusion has occurred based on the sensedpressure.
 7. The dialysis cassette operating method of claim 6, whichincludes determining that the line occlusion has occurred if the sensedpressure increases when pushing the flexible membrane into the pumpchamber.
 8. The dialysis cassette operating method of claim 6, whichincludes determining that the line occlusion has occurred if the sensedpressure fails to meet an expected pressure drop when pushing theflexible membrane into the pump chamber.
 9. The dialysis cassetteoperating method of claim 6, which includes determining that the lineocclusion has occurred during a priming sequence.
 10. The dialysiscassette operating method of claim 6, which includes pulling a vacuum onthe flexible membrane, opening the membrane within the pump chamber tofill the pump chamber with the fluid.
 11. The dialysis cassetteoperating method of claim 6, wherein directly sensing the pressureincludes contacting the flexible membrane with a pressure sensor.
 12. Amethod for operating a dialysis cassette including a flexible membranethat covers a pump chamber, the method comprising: filling the pumpchamber with fluid; monitoring movement of a piston head pushing theflexible membrane into the pump chamber; and determining that a leak inthe dialysis cassette has occurred if the piston head moves when thepiston head is expected to remain stationary.
 13. The dialysis cassetteoperating method of claim 12, wherein pushing the flexible membranecauses the piston head to apply a force to the flexible membrane, theleak enabling the piston head to move the membrane.
 14. The dialysiscassette operating method of claim 12, which includes pulling a vacuumon the flexible membrane, opening the membrane within the pump chamberto fill the pump chamber with the fluid.
 15. A dialysis machinecomprising: a housing; a mechanically actuated piston head extendingfrom a pump actuator housed by the housing, the mechanically actuatedpiston head positioned to extend towards and away from a fluid pumpingcassette, the fluid pumping cassette coupled operably to the housingsuch that a flexible membrane of the fluid pumping cassette faces thepiston head so that the piston head can push the flexible membrane intoa pump chamber of the fluid pumping cassette to expel a fluid from thepump chamber; a pressure sensor located adjacent to the mechanicallyactuated piston head so as to sense a pressure of the fluid moved by themechanically actuated piston head within the fluid pumping cassette; anda controller programmed to use the sensed pressure to perform a testprior to delivering fluid to a patient.
 16. The dialysis machine ofclaim 15, wherein the test determines whether a line occlusion hasoccurred.
 17. The dialysis machine of claim 15, which includes a vacuumchamber configured to pull a vacuum on the flexible membrane to open themembrane within the pump chamber to fill the pump chamber with thefluid.
 18. The dialysis machine of claim 15, wherein the pressure sensordirectly senses the pressure of the fluid flowing through a flow path ata location of the fluid pumping cassette between the pump chamber and aflow path valve.
 19. The dialysis machine of claim 15, wherein thepressure sensor contacts the flexible membrane.
 20. A dialysis machinecomprising: a housing; a mechanically actuated piston head extendingfrom a pump actuator housed by the housing, the mechanically actuatedpiston head positioned to extend towards and away from a fluid pumpingcassette, the fluid pumping cassette coupled operably to the housingsuch that a flexible membrane of the fluid pumping cassette faces thepiston head so that the piston head can push the flexible membrane intoa pump chamber of the fluid pumping cassette to expel a fluid from thepump chamber; a pressure sensor located adjacent to the mechanicallyactuated piston head so as to sense a pressure of the fluid moved by themechanically actuated piston head within the fluid pumping cassette; anda controller programmed to use the sensed pressure to determine whethera line occlusion has occurred.
 21. The dialysis machine of claim 20,wherein the line occlusion is determined by the controller if the sensedpressure increases when extending the flexible membrane into the pumpchamber.
 22. The dialysis machine of claim 20, wherein the lineocclusion is determined by the controller if the sensed pressure failsto meet an expected pressure drop when extending the flexible membraneinto the pump chamber.
 23. The dialysis machine of claim 20, wherein theline occlusion is determined by the controller during a primingsequence.
 24. The dialysis machine of claim 20, which includes a vacuumchamber configured to pull a vacuum on the flexible membrane to open themembrane within the pump chamber to fill the pump chamber with thefluid.
 25. The dialysis machine of claim 20, wherein the pressure sensorcontacts the flexible membrane.
 26. A dialysis machine comprising: ahousing; a mechanically actuated piston head extending from a pumpactuator housed by the housing, the mechanically actuated piston headpositioned to extend towards and away from a fluid pumping cassette, thefluid pumping cassette coupled operably to the housing such that aflexible membrane of the fluid pumping cassette faces the piston head sothat the piston head can push the flexible membrane into a pump chamberof the fluid pumping cassette to expel a fluid from the pump chamber;and a controller programmed to perform a leak test by monitoring asensed position of the mechanically actuated piston head while themechanically actuated piston head applies a force to the flexiblemembrane of the fluid pumping cassette.
 27. The dialysis machine ofclaim 26, wherein a leak enables the mechanically actuated piston headto move the membrane.
 28. The dialysis machine of claim 26, whichincludes a vacuum chamber configured to pull a vacuum on the flexiblemembrane to open the membrane within the pump chamber to fill the pumpchamber with the fluid.